Ku Y, Jacobsen S B
Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA.
Sci Adv. 2020 Oct 9;6(41). doi: 10.1126/sciadv.abd0511. Print 2020 Oct.
Potassium (K) and other moderately volatile elements are depleted in many solar system bodies relative to CI chondrites, which closely match the composition of the Sun. These depletions and associated isotopic fractionations were initially believed to result from thermal processing in the protoplanetary disk, but so far, no correlation between the K depletion and its isotopic composition has been found. Our new high-precision K isotope data correlate with other neutron-rich nuclides (e.g., Ni and Cr) and suggest that the observed K variations have a nucleosynthetic origin. We propose that K isotope anomalies are inherited from an isotopically heterogeneous protosolar molecular cloud, and were preserved in bulk primitive meteorites. Thus, the heterogeneous distribution of both refractory and moderately volatile elements in chondritic meteorites points to a limited radial mixing in the protoplanetary disk.
相对于与太阳成分密切匹配的CI球粒陨石，许多太阳系天体中的钾（K）和其他中等挥发性元素都有所亏损。这些亏损以及相关的同位素分馏最初被认为是原行星盘中热加工的结果，但到目前为止，尚未发现钾亏损与其同位素组成之间存在相关性。我们新的高精度钾同位素数据与其他富含中子的核素（如镍和铬）相关，这表明观测到的钾变化具有核合成起源。我们提出，钾同位素异常是从同位素不均匀的原太阳分子云继承而来的，并保存在大量原始陨石中。因此，球粒陨石中难熔和中等挥发性元素的不均匀分布表明原行星盘中的径向混合有限。
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